Re: [netmod] yang-instance-file include-defaults leaf

[Balázs Lengyel <[e-mail]>]

Hello Andy,

See below as BALAZS2.

 

From: Andy Bierman <[e-mail]> 
Sent: 2021. augusztus 24., kedd 13:35
To: Balázs Lengyel <[e-mail]>
Cc: Rob Wilton (rwilton) <[e-mail]>; NetMod WG <[e-mail]>
Subject: Re: [netmod] yang-instance-file include-defaults leaf

 

 

 

On Tue, Aug 24, 2021 at 1:41 AM Balázs Lengyel <[e-mail] <mailto:[e-mail]> > wrote:

Hello Andy,

In the -17 I removed the default value for includes-defaults as you proposed.

 

I am not sure I understand the rest of the comments as instance-file-format does not use the concept of “basic-mode”. It has a single leaf to indicate what is the situation with defaults in the specific instance-data-set.

As this is not a live server request/reply situation we do not want to specify a basic and additional modes, we just want to specify the handling used for this specific instance data set.

 

 

The draft as written does not actually provide the same utility as <with-defaults>.

(Without the "default" attribute the "explicit" mode is not actually supported.)

 

The "with-defaults" mechanism works exactly the same no matter what

the XML representation is used for.  The mode used to write the data will

correspond to the basic-mode with the same name.

BALAZS2: I will add the report-all-tagged mode to the leaf includes-defaults. This will include the usage of default attribute in the instance data. Will that make the attribute acceptable for you ?

 

Regards Balazs

 

Andy

 

 

From: Andy Bierman <[e-mail] <mailto:[e-mail]> > 
Sent: 2021. augusztus 23., hétfő 18:58
To: Balázs Lengyel <[e-mail] <mailto:[e-mail]> >
Cc: Rob Wilton (rwilton) <[e-mail] <mailto:[e-mail]> >; NetMod WG <[e-mail] <mailto:[e-mail]> >
Subject: Re: [netmod] yang-instance-file include-defaults leaf

 

 

 

On Mon, Aug 23, 2021 at 5:17 AM Balázs Lengyel <[e-mail] <mailto:[e-mail]> > wrote:

Hello Rob,

I think this won’t fly. 

In sections 1.2 and 2 we state:

“Instance data files MAY contain partial data sets.”
Which is important for many use-cases.  This means you cannot say that a default value will or must be included, as they might be omitted because they are not part of the partial data set.
In a way it is difficult to separate between leaves that are missing because
-        They are not part of the partial data-set
-        They are omitted because they have the default value and one of the trim or explicit options is used
If this becomes important the report-all options shall be used.
 

 

 

I thought we already agreed there cannot be a default or there is no way to

represent "no defaults added".

 

Note that "report-all" is not useful if basic-mode=explicit, since a leaf reporting the YANG default

could be set by the client.  Only report-all-tagged will clearly identify defaults in this case.

 

Also note that if basic-mode=report-all then there will be no defaults ever reported.

This mode means the server does not consider any node to be a default and always returns

every node (if with-defaults used or not).

 

This is the reason I used the SHOULD word.
Regards Balazs

 

Andy

 

 

From: Rob Wilton (rwilton) <[e-mail] <mailto:[e-mail]> > 
Sent: 2021. augusztus 23., hétfő 12:27
To: Balázs Lengyel <[e-mail] <mailto:[e-mail]> >; Andy Bierman <[e-mail] <mailto:[e-mail]> >; NetMod WG <[e-mail] <mailto:[e-mail]> >
Subject: RE: [netmod] yang-instance-file include-defaults leaf

 

Hi Balazs, Andy, Netmod,

 

Sorry for the delayed response.  I would still like to strength the description of the defaults.  E.g., RFC 6243 uses MUSTs rather than SHOULDs.

 

Hence, I have generated some proposed alternative descriptions, that are somewhat stricter, but also more generically focussed only on the default values.

 

With these definitions, I think that we could define the “include-defaults” default value to be “explicit”, since if the leaf if not included, then I think that this effectively what the meaning would be anyway.

 

 

In particular, I would propose changing the descriptions as follows:

 

       leaf includes-defaults {

         type enumeration {

           enum report-all {

             value 1;

             description

               "All data nodes SHOULD be included independent of

                 any default values.";

           }

           enum trim {

             value 2;

             description

               "Data nodes that have a default defined and where

                 the actual value is the default value SHOULD

                 NOT be included.";

           }

           enum explicit {

             value 3;

             description

               "Data nodes that have a default defined and where

                 the actual value is the default value SHOULD NOT be

                 included. However, if the actual value was set by

                 a NETCONF client or other management application

                 by the way of an explicit management operation the

                 data node SHOULD be included.";

           }

         }

      

Proposed:

 

       leaf includes-defaults {

         type enumeration {

           enum report-all {

             value 1;

             description

               "The instance data set includes all data nodes,

                including those that contain the schema default.”;

           }

           enum trim {

             value 2;

             description

               "The instance data set excludes all data nodes

                that contain the schema default.";

           }

           enum explicit {

             value 3;

             description

               "The instance data set may include some data nodes

                that match the schema default and may exclude some

                data nodes that match the schema default.”;

           }

         }

         description

           "This leaf provides an indication of how default data

            is presented within an instance data set, modelled on

            RFC 6243.

 

            Interpretation of the use of defaults depends on the

            context of what the instance data set represents.

 

            E.g., if the instance data set represents configuration,

            Then include-defaults aligns to the meaning of the

            default-handling basic modes in RFC 6243.  If the

            instance data set represents operational data from the 

            operational state datastore [RFC 8342], then

            include-defaults aligns to the definition of that

            datastore in RFC 8342.”;

 

Would text along these lines work?

 

Thanks,

Rob

 

 

From: Balázs Lengyel <[e-mail] <mailto:[e-mail]> > 
Sent: 28 July 2021 23:08
To: Rob Wilton (rwilton) <[e-mail] <mailto:[e-mail]> >; Andy Bierman <[e-mail] <mailto:[e-mail]> >
Cc: NetMod WG <[e-mail] <mailto:[e-mail]> >
Subject: RE: [netmod] yang-instance-file include-defaults leaf

 

Hello Rob,

Removing the “default trim;” will address Andy’s comment.

 

Your in-use-values is very specific to one of the use-cases: reading/documenting operational values. It is not useful for the other use-cases. I think the “documenting operational datastore” use-case could be handled by indicating the includes-defaults=report-all. Case (i) would contain the value case (ii) will not.

Regards Balazs

 

From: Rob Wilton (rwilton) <[e-mail] <mailto:[e-mail]> > 
Sent: 2021. július 27., kedd 17:38
To: Andy Bierman <[e-mail] <mailto:[e-mail]> >; Balázs Lengyel <[e-mail] <mailto:[e-mail]> >
Cc: NetMod WG <[e-mail] <mailto:[e-mail]> >
Subject: RE: [netmod] yang-instance-file include-defaults leaf

 

Hi Andy, Balazs,

 

So, the reason that I want a flag to indicate whether default values are in use is because of this definition of operational in RFC 8342:

 

   Requests to retrieve nodes from <operational> always return the value

   in use if the node exists, regardless of any default value specified

   in the YANG module.  If no value is returned for a given node, then

   this implies that the node is not used by the device.

 

It was written this way because otherwise a consumer of operational data cannot differentiate between:

(i)               This value is not present because it matches the default value specified in the YANG module, and

(ii)              This value is not present because the server has failed to return it for some reason (e.g., perhaps the daemon that would have provided this value is down or not available, or perhaps it is a bug, or perhaps it is not implemented and is a missing deviation).

 

So, I think that in some cases, the absence of a data node does not necessarily mean that the default value is in effect, and I wanted the instance-data document to be able to contain and correctly report this data.

 

I think that this behaviour could be captured by a single leaf.  Another way of articulating this would be:

 

leaf in-use-values {

  type boolean;

  default false;

  description

    “Only if set to true, the absence of a value in the

     instance data for a given data node implies that the

    node is not used rather than implicitly taking the

     default value specified by any corresponding

    ‘default’ statement specified in the YANG schema.”;

}

 

With this, I’m not sure whether we need the “includes-default” leaf currently specified in the draft, but if we do, then I would think that leaf should be entirely optional, i.e., without the default “trim”.

 

Regards,
Rob

 

 

From: Andy Bierman <[e-mail] <mailto:[e-mail]> > 
Sent: 10 July 2021 17:41
To: Rob Wilton (rwilton) <[e-mail] <mailto:[e-mail]> >
Cc: NetMod WG <[e-mail] <mailto:[e-mail]> >; Balázs Lengyel <[e-mail] <mailto:[e-mail]> >
Subject: Re: [netmod] yang-instance-file include-defaults leaf

 

 

 

On Fri, Jul 9, 2021 at 5:23 AM Rob Wilton (rwilton) <[e-mail] <mailto:[e-mail]> > wrote:

Andy,

 

Yes, when I suggested this, I was thinking that a boolean flag might be sufficient.  My point being that automatically filtering out default values isn’t always the right thing to do.

 

 

 

The solution is simple.

Get rid of the inappropriate "default trim" statement.

 

If the leaf is present then it identifies the basic-mode that was used to include defaults.

If not then the information is either not known, not applicable, or defaults were not added.

 

The "default" statement is a bug because there is no default basic-mode.

All of the basic-modes are in use in deployments and no camp has ever

been able to convince the others that theirs is right.

 

 

Andy

 

E.g., something along these lines:

 

leaf exclude-defaults {

  type boolean;

  default true;

  description

    “Can be used to reduce the size of the content data file.

 

      When unset or set to true, data nodes that have a default defined and

      where the actual value is the default value are excluded from the content

      data.

 

      When set to false, data nodes with default value are not filtered, and

      may appear in the content data.”

}

 

Would this satisfy your concern?

 

Regards,
Rob

 

 

From: netmod <[e-mail] <mailto:[e-mail]> > On Behalf Of Andy Bierman
Sent: 08 July 2021 18:16
To: NetMod WG <[e-mail] <mailto:[e-mail]> >
Subject: [netmod] yang-instance-file include-defaults leaf

 

Hi,

 

The module has this object:

 

    leaf includes-defaults {
       type enumeration {
         enum report-all {
           value 1;
           description
             "All data nodes SHOULD be included independent of
               any default values.";
         }
         enum trim {
           value 2;
           description
             "Data nodes that have a default defined and where
               the actual value is the default value SHOULD
               NOT be included.";
         }
         enum explicit {
           value 3;
           description
             "Data nodes that have a default defined and where
               the actual value is the default value SHOULD NOT be
               included. However, if the actual value was set by
               a NETCONF client or other management application
               by the way of an explicit management operation the
               data node SHOULD be included.";
         }
       }
       default trim;
 

The draft is extremely server-centric, like most IETF standards, but this

leaf is too server-centric to ignore.

 

Consider the possibility that the source of the file is NOT a NETCONF server.

This data may not be known so the default of "trim" may not be correct.

 

IMO this leaf is noise because any tool that knows the schema will also

know the YANG defaults.  The solution is incomplete anyway because

the presence of a leaf that has a YANG default is not enough.

The  "report-all-tagged" mode must be used to identify defaults.

IMO this leaf should be removed, but at least add an enum called "unknown".

 

 

Andy